This invention relates to an upper thread-hooking method for an industrial machine. Particularly, the invention is directed to a hooking member of an upper thread-hooking device that does not occupy the gap between a needle point and the presser foot, so that the thickness of a cloth to be sewn may be as thick as possible, and the hooking member will not collide with a needle during operation of the hooking member.
A conventional upper thread-hooking device of a sewing machine is shown in FIGS. 6-10, including an electronic component 11, a side plate 12 fixed on a side of the electronic component 11, a main sway arm 13, and an auxiliary sway arm 14 as main components.
The side plate 12 has a curved slot 121 in an intermediate portion sloping down for a screw to insert to connect an upper end 132 of the main sway arm 13 with the side plate 12. A curved horizontal hole 122 is formed at the left side of the curved slot 121 for connecting an upper end 141 of the auxiliary sway arm 14 with an outer end of the connecting rod of the electronic component 11 with a bolt 143 and a nut 122. The intermediate section 134 of the main sway arm is connected to a second end of the auxiliary sway arm 14, which has a bent corner 142 fixed with the side plate 12 with a bolt 143 and a nut 122, with the bolt 143 functioning as a pivot for the auxiliary sway arm 14 to sway. Then the first end 141 of the auxiliary sway arm 14 may be connected to a function end 111 of the connecting rod of the electronic component 11.
In operation of the upper thread-hooking device of the conventional sewing machine, when the needle 15 is raised to the highest point, the electronic component 11 is powered to let the connecting rod pull the function end 111, and the auxiliary sway arm 14 moves along the curved hole 122 to the other end. Thus, the auxiliary sway arm 14 restrains the main sway arm 13 to move down along the curved slot 121 so that the hooking member 131 can hook back the thread 16 carried by the needle in sewing. Then, the thread 16 is cut off by a cutter under the slide plate 1, and the other end of the thread carried by the needle 15 is caught between the two front plate springs 131 to keep the front short end of the thread 16 on the slide plate when the needle 15 makes another sewing cycle, for leaving no front end of the thread in the sewing process.
The greatest advantage of the conventional upper thread-hooking device is that the front end of the thread is hidden, not completely exposed. When the needle 15 rises to the highest point, the hooking in the gap between the needle point and the presser foot occurs, hooking the thread 16 again to the right side.
However, the above mentioned hooking method still has drawbacks in practical use, as follows.
1. The presser foot presses cloth during sewing, and is at different levels in accordance with the thickness of the cloth being sewn, so the gap between the needle point and the presser foot may vary accordingly. Thus, the gap may become very small for the hooking member to pass through, but the gap between the needle point and the slide plate is definite and unchangeable, when the needle rises to the highest point. So, that creates a limit in using this conventional upper thread hooking device, as shown in FIGS. 9 and 10.
2. As the hooking member is located directly under the needle point and performs the hooking action in the gap between the needle point and the presser foot, there should be an ample gap to permit the whole hooking member to move with a safety tolerance, so that the hooking member will not collide with the needle point or the presser foot, as shown in FIG. 10. Consequently, the rising distance of the presser foot is limited after the hooking member is installed. Then, the range of thickness of cloth to be sewn will be decreased. It a cloth that is too thick is used, the hooking member may collide with the presser foot or the needle.
3. The needle is located at a very high point in some types of industrial sewing machines, and the gap between the needle point and the slide plate may be 8 mm (in such machines as the BROTHER FD4-B272) for sewing comparatively thick cloth used in winter clothing. But the hooking member and the safe tolerance needs about 3 mm. So this kind of industrial sewing machine is still not so suitable for use with thick cloth used for winter clothing. The automatic sewing operation and the hooking device with the thread end hidden, of this type, cannot be used as such, but performed by manual operation.